Document reading apparatus and related data transfer method

ABSTRACT

A document reading apparatus includes a conveying unit configured to continuously convey a document having a series of sheets along a conveyance path, a reading unit configured to obtain image data by reading a sheet at a predetermined reading position, a storage unit configured to store the image data obtained by the reading unit, and a transfer unit configured to transfer the stored image data to a transfer destination. The transfer satisfies a relationship X+Y≧Z&gt;X, wherein X represents a reading time required for the reading unit to read said sheet, Y represents an interval time between an end of reading said sheet and a beginning of reading a next sheet of the series, and Z represents a transfer time required for the transfer unit to transfer the image data stored in the storage unit to the transfer destination. A related method is also disclosed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a document reading apparatus capable ofreading a document which moves along a predetermined conveyance path anda related data transfer method.

2. Description of the Related Art

Conventionally, a document reading apparatus can be installed on orincorporated into a digital copying machine, a facsimile machine, or ascanner device. A document reading apparatus installed on a copyingmachine which operates in a “document feeding-reading” mode is known.According to this operation mode, the sheets of a document stacked on adocument tray are conveyed one after another to a document positioningglass plate, each sheet is exposed by an exposure apparatus fixed on aconveyance path, and an image of the exposed sheet is read by an imagesensor.

In recent years, to improve the reading efficiency of the documentreading apparatus that performs the above-described documentfeeding-reading operation, it has been effective to reduce a distancebetween two consecutive sheets (referred to as “sheet-to-sheetinterval”) when the sheets stacked on the document tray are conveyed oneafter another along a conveyance path. This technique can increase thenumber of readable sheets per unit time.

For example, as discussed in Japanese Patent Application Laid-Open No.2005-324872, the sheet-to-sheet interval can be reduced by quicklystarting a feeding operation of a sheet upon detecting the trailing edgeof a preceding sheet. The conveying speed of a document can be reducedwithout deteriorating the reading efficiency.

However, according to the above-described conventional document readingapparatus, the following problems occur if a plurality of sheets iscontinuously read and read image data are transferred in real-time to aprinter connected to the document reading apparatus.

Namely, to keep a certain sheet interval between a preceding sheet and afollowing sheet, the time available for transferring the image databecomes shorter. Thus, the image data needs to be transferred at a clockfrequency higher than a pre-designated clock frequency required toattain an intended reading efficiency.

If the entire system operates at a higher clock frequency, variousproblems (e.g., temperature rise, increase in electric powerconsumption, and generation of radiation noises) occur. Realizing atiming design for an application specific integrated circuit (ASIC) orother IC that performs image processing also becomes difficult.

SUMMARY OF THE INVENTION

The present invention is directed to a document reading apparatus whichenables an entire system to operate at a lower clock frequency whileimproving an efficiency of reading a plurality of sheets. Furthermore,the present invention is directed to a related data transfer method.

According to an aspect of the present invention, a document readingapparatus is capable of conveying a document having a series of sheetsalong a conveyance path and of reading each sheet of the series at apredetermined reading position on the conveyance path. The documentreading apparatus includes a conveying unit configured to continuouslyconvey the document along the conveyance path, a reading unit configuredto obtain image data by reading a sheet of the series at thepredetermined reading position, a storage unit configured to store theimage data obtained by the reading unit, and a transfer unit configuredto transfer the stored image data to a transfer destination. Inaccordance with the aspect, the transfer unit transfers the image datato the transfer destination to satisfy a relationship X+Y≧Z>X, wherein Xrepresents a reading time required for the reading unit to read saidsheet of the series, Y represents an interval time between an end ofreading said sheet of the series and a beginning of reading a next sheetof the series, and Z represents a transfer time required for thetransfer unit to transfer the image data stored in the storage unit tothe transfer destination.

According to another aspect of the present invention, a method isprovided for a document reading apparatus capable of conveying adocument having a series of sheets along a conveyance path and readingeach sheet of the series at a predetermined reading position on theconveyance path. The method includes conveying the document continuouslyalong the conveyance path; obtaining image data by reading a sheet ofthe series at the predetermined reading position; storing the obtainedimage data into a storage medium; and transferring the stored image datato a transfer destination. Moreover, the image data is transferred tothe transfer destination to satisfy a relationship X+Y≧Z>X, wherein Xrepresents a reading time required for reading said sheet of the series,Y represents a document interval time between an end of reading saidsheet of the series and a beginning of reading a next sheet of theseries, and Z represents a transfer time required for transferring theimage data stored in the storage medium to the transfer destination.

Further features and aspects of the present invention will becomeapparent from the following detailed description of exemplaryembodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate exemplary embodiments and featuresof the invention and, together with the description, serve to explain ofthe principles of the present invention.

FIG. 1 illustrates a cross-sectional view of an example document readingapparatus according to an exemplary embodiment of the present invention.

FIG. 2 is a block diagram illustrating an example control unit of animage processing system according to an exemplary embodiment of thepresent invention.

FIG. 3 is a flowchart illustrating an example conveying operationprocedure performed by an automatic document feeder according to anexemplary embodiment of the present invention.

FIG. 4 is a flowchart illustrating an example document reading procedureaccording to an exemplary embodiment of the present invention.

FIG. 5 illustrates an example operation for conveying a plurality ofdocuments.

FIG. 6 illustrates an example transfer of image data.

FIG. 7 illustrates an example transfer of image data in a case whereimage data transfer can be performed during a document conveyinginterval.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following description of exemplary embodiments of the presentinvention is illustrative in nature and is in no way intended to limitthe invention, its application, or uses. Throughout the specification, arepeated reference mark refers to the same item (or alternativelysimilar items) where it appears in more than place. Once an item isdescribed in one figure, it may not be described further for theremaining figures where such further description would be redundant.Exemplary embodiments are described in detail below with reference tothe drawings.

First Exemplary Embodiment

FIG. 1 illustrates a cross-sectional view of a document readingapparatus 10 according to an exemplary embodiment of the presentinvention. The document reading apparatus 10 can be installed on orincorporated into a digital copying machine, a facsimile machine, ascanner device, or other device which includes an automatic documentfeeder capable of continuously conveying a document having a pluralityof sheets.

The document reading apparatus 10 includes an automatic document feeder100 and a reader unit 200. The reader unit 200 is configured to read animage on each document conveyed from the automatic document feeder 100which can continuously convey a plurality of documents. The automaticdocument feeder 100 includes a document tray 101 on which the sheets ofthe document 102 can be stacked. A sheet feeding roller 103 ispositioned near the document tray 101.

The sheet feeding roller 103 and a separation/conveyance roller 104 areconnected to a common driving source that can drive the rollers 103 and104 to feed the document 102. The sheet feeding roller 103 is initiallypositioned at a retreated home position (upper position) where the sheetfeeding roller 103 does not interfere with a user who sets the documents102. If the automatic document feeder 100 starts a sheet feedingoperation, the sheet feeding roller 103 moves downward and contacts anuppermost sheet of the document 102. The sheet feeding roller 103 canmove in the up-and-down direction in accordance with a swing motion ofarms (not illustrated) which support a shaft of the sheet feeding roller103.

A separation/conveyance roller 105 is located facing theseparation/conveyance roller 104 and pressed against theseparation/conveyance roller 104. The separation/conveyance roller 105is made of a rubber member capable of generating a frictional forceslightly smaller than that of a member constituting theseparation/conveyance roller 104. The separation/conveyance roller 105is indirectly driven by means of frictional force. Theseparation/conveyance rollers 104 and 105 cooperate to separate theuppermost sheet of the stacked documents 102 and convey the separateddocument 102 one sheet after another along a conveyance path when theplurality of sheets of the document 102 are fed from the document tray101 via the sheet feeding roller 103.

A registration roller 106 and a driven registration roller 107 (i.e., aregistration roller pair) align a leading edge of the document 102separated and conveyed by the separation/conveyance rollers 104 and 105.If the leading edge (i.e., front edge) of the separated document 102abuts a nip portion of the registration roller pair 106 and 107 which isin a stationary state, the leading edge of the document 102 is alignedwhile the document 102 deforms in a loop shape.

A lead roller 108 and a driven lead roller 109 cooperatively convey thedocument 102 toward a document feeding-reading glass 116. A platenroller 110 is disposed facing the document feeding-reading glass 116.When a sheet of the document 102 moves across the documentfeeding-reading glass 116, a charge coupled device (CCD) line sensor 126reads an image on the sheet.

After the CCD line sensor 126 completes an image reading operation, alead discharge roller 111 and a driven lead discharge roller 112cooperatively convey the sheet of the document 102 toward a sheetdischarge roller 113. The sheet discharge roller 113 discharges thesheet of the document 102 to a sheet discharge tray 114. This process isrepeated for each sheet of the document.

The reader unit 200 includes a lamp 119, three mirrors 120, 121, and122, a lens 125, and the CCD line sensor 126. The lamp 119 emits lighttoward a surface of the document 102 to be read. The mirrors 120, 121,and 122 sequentially reflect the reflection light from the document 102and guide the reflection light toward the lens 125 and the CCD linesensor 126. Both the lamp 119 and the mirror 120 are mounted on a firstmirror base 123. The mirrors 121 and 122 are mounted on a second mirrorbase 124.

The first mirror base 123 and the second mirror base 124 which arerespectively connected to a driving motor (not illustrated) via a wire(not illustrated) can move horizontally in parallel with a documentpositioning glass plate 118 when the driving motor rotates. Thereflection light from the document 102 is guided toward the lens 125 bythe mirrors 120, 121, and 122. The light having passed through the lens125 forms an image on a light-receiving portion of the CCD line sensor126. The CCD line sensor 126 photoelectrically converts the reflectionlight (the formed image) by a light-sensitive element and outputs anelectric signal representing a quantity of incident light at eachportion or pixel of the image. The document reading apparatus 10optionally may include color scanning capabilities, in which case, anelectrical signal additionally indicates the color at each portion orpixel of the image.

The document reading apparatus 10 has two operation modes, a documentfixed-reading mode and a document feeding-reading mode, which areselectable by a user. In the document fixed-reading mode, the documentreading apparatus 10 reads an image on a sheet of the document 102 whichis manually set by a user on the document positioning glass plate 118,while the first mirror base 123 and the second mirror base 124 move inthe sub-scanning direction (i.e., in the direction indicated by an arrow“a” in FIG. 1).

In the document feeding-reading mode, the document reading apparatus 10reads a respective image on each sheet of the document 102 which isautomatically supplied from the automatic document feeder 100. Thereading occurs at a pre-determined position of the documentfeeding-reading glass 116 (i.e. document reading position,) while thefirst mirror base 123 and the second mirror base 124 are stopped.

The document conveying interval is described below. The time requiredfor the separation/conveyance roller 104 and the drivenseparation/conveyance roller 105 to separate a sheet of the document 102fed by the sheet feeding roller 103 from the document tray 101 isvariable depending on surface qualities of the document 102. The leadingedge of separated and conveyed sheet of the document 102 is then alignedby the registration roller 106 and the driven registration roller 107.Then, the sheet of the document 102 is conveyed by the lead roller 108and the driven lead roller 109 toward the document feeding-reading glass116.

An interval between a sheet of the document and a next sheet of thedocument is determined considering a variation in the above-describedtime required for separating the sheets of the document 102. Namely, theautomatic document feeder 100 controls a document feeding operation tokeep the constant interval between sequential pairs of sheets which areconsecutively conveyed. In this exemplary embodiment, the documentconveying interval is set to 40 mm.

FIG. 2 is a block diagram illustrating a control unit 300 of an imageprocessing system according to an exemplary embodiment of the presentinvention. The control unit 300 includes an analog-to-digital (A/D)conversion circuit 301, a shading correction circuit 302, a temporarystorage memory 303, a pulse generator circuit 305, an image datatransfer line 307, a central processing unit (CPU) 309, and the CCD linesensor 126.

The pulse generator circuit 305 generates a pulse to drive the CCD linesensor 126 that reads a surface of the document 102. The A/D conversioncircuit 301 receives an analog signal from the CCD line sensor 126 andconverts the received signal into a digital signal. The shadingcorrection circuit 302 performs a shading correction on image data(i.e., the digital signal produced by the A/D conversion circuit 301).

The temporary storage memory 303 (i.e., a storage medium) temporarilystores the image data having been subjected to the shading correction.The image data stored in the temporary storage memory 303 can betransferred via the image data transfer line 307 to a processing circuit401. The processing circuit 401 is a transfer destination and may be,for example, a printer or a computer.

The CPU 309 controls a document reading operation. The CPU 309 canchange a driving speed of the CCD line sensor 126 which can be set inthe pulse generator circuit 305 as well as a transfer speed of datatransferred from the temporary storage memory 309 to the processingcircuit 401.

The above-described document reading apparatus can, for example, performthe following operation. FIG. 3 is a flowchart illustrating an exampleconveying operation procedure performed by the automatic document feeder100 according to an exemplary embodiment of the present invention.

First, in step S1, the automatic document feeder 100 drives the sheetfeeding roller 103 to convey the uppermost sheet of the document 102which is placed on the document tray 101 to the separation/conveyanceroller pair 104 and 105.

In step S2, if two or more sheets of the document 102 are simultaneouslyconveyed, the automatic document feeder 100 drives theseparation/conveyance rollers 104 and 105 to separate a sheet ofdocument 102.

In step S3, the automatic document feeder 100 conveys the separatedsheet of the document 102 to a downstream side where the registrationroller pair 106 and 107 aligns the leading edge of the separated sheetof the document 102 and guides the separated sheet of the document 102to a gap between the lead roller pair 108 and 109. Then, the separatedsheet of the document 102 is conveyed to the document reading position(document reading unit).

In step S4, the automatic document feeder 100 drives the lead dischargerollers 111 and 112 to convey the separated sheet of the document 102having been subjected to the reading operation.

In step S5, the automatic document feeder 100 drives the sheet dischargeroller 113 to discharge the separated sheet of the document 102 to thesheet discharge tray 114. As described above, in the document conveyingoperation performed by the automatic document feeder 100, the intervalbetween two consecutively conveyed sheets of the document 102 iscontrolled to be a constant value (e.g., 40 mm).

FIG. 4 is a flowchart illustrating an example document reading procedureaccording to an exemplary embodiment of the present invention.

In step S11, the document reading apparatus 10 starts the documentconveying operation described with reference to the flowchartillustrated in FIG. 3.

In step S12, if a sheet of the document 102 reaches the document readingposition, the document reading apparatus 10 causes the CCD line sensor126 to start reading an image on the sheet of the document 102 andstores the read image data in the temporary storage memory 303.Concurrently, the document reading apparatus 10 starts reading out theimage data from the temporary storage memory 303 and transferring imagedata to the processing circuit 401 via the image data transfer line 307.

In step S13, the document reading apparatus 10 determines whether theabove-described transfer operation for reading out the image data fromthe temporary storage memory 303 and transferring the read image datavia the image data transfer line 307 has been completed. If the transferoperation has not been completed (NO in step S13), the document readingapparatus 10 repeats the above-described processing of step S12. It isnot necessary in this repetition of step S12 to rewrite image data intothe temporary storage memory 303 as the un-transferred portion of thealready stored data for the sheet continues to be stored at least untilthe transfer operation for that sheet is complete.

If the transfer operation has been completed (YES in step S13), theprocedure proceeds to step S14. In step S14, the document readingapparatus 10 determines whether the next sheet of the document 102 ispresent. If a next sheet of the document is present (YES in step S14),the document reading apparatus 10 returns to step S12 to process thatnext sheet. However, if a next sheet of the document 102 is not present(NO in step S14), the document reading apparatus 10 completes thedocument reading operation.

The document conveying speed and the driving speed of the CCD linesensor 126 are in the following relationship. It is now assumed that thedocument reading apparatus operates at a driving speed capable ofreading 60 sheets of A4 document per minute. If a document reading speedis constant, the document reading operation needs to be performed at aspeed of reading one sheet per second.

The sub-scanning length for A4 size is 210 mm. If the document conveyinginterval (sheet-to-sheet interval) is set to 40 mm, the CCD line sensor126 needs to be driven at a reading speed of 250 mm per second.

It is now assumed that the document reading operation is performed atthe resolution of 600 dots per inch (dpi). According to theabove-described conditions, the scanning time per sub-scanning line canbe obtained according to the following formula (1).

One sub-scanning line time=1 sec/(250 mm/(25.4 mm/600))   (1)

Namely, it can be understood that the driving speed of the CCD linesensor 126 is required one sub-scanning line time=169 μsec.

Furthermore, if the CCD line sensor 126 is driven under theabove-described conditions, the sub-scanning magnification becomes 100%when the conveying speed of each document conveying roller is 250 mm persecond. Therefore, a required conveying speed of each roller is equal to250 mm/sec.

FIG. 5 illustrates an example operation for conveying a series of sheetsof the document 102. The main scanning time is described below. The CCDline sensor 126 includes light-sensitive elements for 7200 pixels thatcan attain 600 dpi resolution in a reading operation of A4 document. Themain scanning length for A4 size is 297 mm. Therefore, an effective areafor reading actual document image data on a sheet of the A4 document isapproximately 7016 pixels.

If the CCD line sensor 126 is a CCD type linear sensor, a non-effectivearea period of approximately 10 μsec is required. The non-effective areaperiod is, for example, a shift transfer period during which electriccharge is transferred from a photodiode to a CCD transfer register. Thenumerical value of the non-effective area period is variable dependingon the CCD type.

Therefore, the time required for transferring one pixel can be obtainedaccording to the following formula (2).

Transfer period for one pixel=(169−10)/7200   (2)

Namely, transfer period for one pixel=22.08 nsec (45.28 MHz).

Here, the transfer speed of image data transferred via the image datatransfer line 307 is described below. It is now assumed that the CCDline sensor 126 is driven at a reading speed of 250 mm per second andthe image data captured by the CCD line sensor 126 is directlytransferred to the image data transfer line 307 without beingtemporarily stored in the temporary storage memory 303.

FIG. 6 illustrates an example transfer of image data. In this example,the document conveying interval is 40 mm and the length of an areacapable of actually transferring effective data to the image datatransfer line 307 is limited to 210 mm. Furthermore, the reading time Xrequired for reading a sheet of the document 102 is 0.81 sec, and thedocument interval time Y between a sheet of the document 102 and a nextsheet of the document 102 is 0.19 sec when the aforementioned next sheetof the document 102 is conveyed to the document reading position.

Next, it is assumed that image data captured by the CCD line sensor 126is stored in the temporary storage memory 303 and a time for thedocument conveying interval of 40 mm can be used for the transfer ofimage data. In this example, it is unnecessary to consider the presenceof document conveying interval. Therefore, the transfer time for onesub-scanning line can be obtained according to the following formula(3).

Transfer time for one sub-scanning line=1 sec/(210 mm/(25.4 mm/600))  (3)

Namely, it is required to transfer the image data to the processingcircuit during the obtained transfer time for one sub-scanning line(=201.59 μsec).

Furthermore, the main scanning time is described below. The timerequired for transferring the data of one pixel (i.e., one of 7200pixels) can be obtained according to the following formula (4).

Transfer period for one pixel=201.59/7200   (4)

Namely, transfer period for one pixel=28.00 nsec (35.72 MHz) Therefore,the data transfer clock can be greatly reduced.

FIG. 7 illustrates an example transfer of image data in a case whereimage data transfer can be performed during a document conveyinginterval. In this example, values X, Y, and Z are set to satisfy arelationship X+Y=Z, wherein X represents a reading time required forreading a sheet of document, Y represents a document interval timebetween a sheet of the document 102 and a next sheet of the document 102when a plurality of sheets of the document are conveyed to the documentreading position, and Z represents a transfer time required fortransferring the image data stored in the temporary storage memory 303to the image data transfer line 307.

Therefore, the CPU 309 controls the pulse generator circuit 305 so as tosatisfy the above-described conditions (i.e., the driving speed of theCCD line sensor 126 and the data transfer speed from the temporarystorage memory 303 to the processing circuit 401). Thus, the presentexemplary embodiment can greatly reduce the data transfer time.

In this case, a required capacity of the temporary storage memory 303corresponds to a speed difference between the driving speed of the CCDline sensor 126 and the data transfer speed to the data transfer line307. Namely, if the document interval of 40 mm is set in a readingoperation of the document of A4 size, the required memory capacity ofthe temporary storage memory 303 will be 40 mm (945 line)×7200 pixels×8bits (=6.9 Mbyte).

In the above-described exemplary embodiment, the transfer time Z is setto satisfy the relationship X+Y=Z. However, optionally a relationshipX+Y≧Z>X can be satisfied to obtain similar effects.

As described above, the document reading apparatus according to thepresent exemplary embodiment can reduce the data transfer speed (i.e.,the speed for transferring data to the data transfer line) compared tothe driving speed of the CCD line sensor. Therefore, the presentexemplary embodiment can reduce the operation speed of the processingcircuit (e.g., a printer or a computer) which is provided at adownstream side of the document reading apparatus. Furthermore, thepresent exemplary embodiment can reduce various problems (e.g.,temperature rise, increase in electric power consumption, and generationof radiation noises) which occur when the document reading apparatusoperates at a higher clock frequency.

As described above, the document reading apparatus according to thepresent exemplary embodiment enables the entire system to operate at alower clock frequency while improving an efficiency of reading aplurality of sheets of a document. Therefore, the above-describedexemplary embodiment can facilitate a timing design for the IC thatperforms image processing. Furthermore, the document reading apparatusaccording to the present exemplary embodiment can perform an efficientdata transfer operation while suppressing temperature rise, electricpower consumption, and radiation noises.

The present invention is not limited to the above-described readingapparatus that operates in the “document feeding-reading” mode. Thepresent invention can be also applied to a document reading apparatusthat operates in the “document fixed-reading” mode according to which areading unit moves in the sub-scanning direction to read an image of adocument sheet set stationary on a document positioning glass plate.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all modifications, equivalent structures, and functions.

This application claims priority from Japanese Patent Application No.2007-109497 filed Apr. 18, 2007, which is hereby incorporated byreference herein in its entirety.

1. A document reading apparatus capable of conveying a document having aseries of sheets along a conveyance path and reading each sheet of theseries at a predetermined reading position on the conveyance path, thedocument reading apparatus comprising: a conveying unit configured tocontinuously convey the document along the conveyance path; a readingunit configured to obtain image data by reading a sheet of the series atthe predetermined reading position; a storage unit configured to storethe image data obtained by the reading unit; and a transfer unitconfigured to transfer the stored image data to a transfer destination,wherein the transfer unit transfers the image data to the transferdestination to satisfy a relationship X+Y≧Z>X, wherein X represents areading time required for the reading unit to read said sheet of theseries, Y represents an interval time between an end of reading saidsheet of the series and a beginning of reading a next sheet of theseries, and Z represents a transfer time required for the transfer unitto transfer the image data stored in the storage unit to the transferdestination.
 2. The document reading apparatus according to claim 1,further comprising a pulse generator circuit configured to generate adriving pulse for driving the reading unit at a predetermined drivingspeed, wherein the driving speed of the reading unit, set in the pulsegenerator circuit, is changeable.
 3. The document reading apparatusaccording to claim 2, wherein the storage unit has a storage capacityequal to or greater than a capacity comparable to a speed differencebetween the driving speed of the reading unit and a transfer speed ofthe transfer unit.
 4. The document reading apparatus according to claim1, wherein the transfer unit performs an operation for transferring theimage data from the storage unit to the transfer destination,concurrently with an operation for storing the image data into thestorage unit.
 5. The document reading apparatus according to claim 1,wherein the reading unit is configured to obtain a series of image datathat respectively corresponds to the series of sheets by reading eachsheet of the series at the predetermined reading position; the storageunit is configured to store the series of image data obtained by thereading unit; and the transfer unit is configured to transfer the storedimage data to the transfer destination; and wherein the transfer unittransfers the series of image data to the transfer destination one sheetat a time so as to satisfy the relationship X+Y≧Z>X for each of thesheets of the series having a next sheet.
 6. A method for a documentreading apparatus capable of conveying a document having a series ofsheets along a conveyance path and reading each sheet of the series at apredetermined reading position on the conveyance path, the methodcomprising: conveying the document continuously along the conveyancepath; obtaining image data by reading a sheet of the series at thepredetermined reading position; storing the obtained image data into astorage medium; and transferring the stored image data to a transferdestination, wherein the image data is transferred to the transferdestination to satisfy a relationship X+Y≧Z>X, wherein X represents areading time required for reading said sheet of the series, Y representsa document interval time between an end of reading said sheet of theseries and a beginning of reading a next sheet of the series, and Zrepresents a transfer time required for transferring the image datastored in the storage medium to the transfer destination.
 7. The methodof claim 6, further comprising repeating the obtaining, storing, andtransferring for each of the sheets of the series having a next sheet,thereby satisfying the relationship X+Y≧Z>X for each sheet of the serieshaving a next sheet.